Organic light-emitting displays (OLED) are one of hotspots in the research field of flat panel display today. Compared with liquid crystal displays, OLEDs have advantages such as low energy consumption, a low production cost, self-illumination, a wide angle of view, a fast response speed or the like. Currently, in the display field of mobile phones, PDAs, digital cameras or the like, OLEDs have begun to replace traditional Liquid Crystal Display (LCD) screens. Design of a pixel driving circuit is the core technical content for OLEDs, and is of important research significance.
Compared with Thin Film Field Effect Transistor (TFT)-LCDs using a stable voltage to control brightness, OLEDs belong to current drive, and need stable current to control light emitting.
Due to process flows and aging of devices or the like, in the existing 2T1C driving circuit (comprising two thin film field effect transistors and one capacitor), threshold voltages of driving TFTs of various pixel points are non-uniform, which leads to a variation in current flowing through OLEDs of various pixels, and makes the display brightness non-uniform, thereby influencing the display effect of the whole image.
A solution for the above problem is to arrange a threshold voltage compensation loop in each pixel circuit to compensate for the threshold voltage of the driving TFT, so that a magnitude of the current flowing through the OLED is unrelated to the threshold voltage. However, if a voltage compensation loop is arranged in each pixel circuit, an area of a single pixel may increase, which results in reduction in a number of Pixels per Inch (PPI) of a corresponding display apparatus.